1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to an IPS (In-Plane Switching) liquid crystal display that is large in area and exhibits a wide viewing angle.
Conventional TFT LCDs (thin film transistor liquid crystal display) have a drawback known as a viewing angle dependency, that is, the contrast ratio is changed according to the viewing angle. This has made it difficult to apply the technology to a large size display.
To solve this problem, various liquid crystal displays have been proposed, such as a retardation attaching TNLCD (twisted nematic liquid crystal display) and a multi-domain liquid crystal display. These LCDs still have other technical problems such as complicated production process and shifting color tones.
2. Discussion of the Related Art
Recently, an IPS LCD has been introduced to obtain a wide viewing angle. This technology is discussed in JAPAN DISPLAY 92, p 547, Japanese patent application No. 7-36058, Japanese patent application No. 7-225538, and ASIA DISPLAY 95, p 707. As shown in FIG. 1a and FIG. 1c, in the liquid crystal layer 12 the molecules are aligned at a 45° angle. The principal transmittance axis of a polarizer 9 attached to the first substrate 1 is the same direction as the alignment direction of the liquid crystal 12, and the principal transmittance direction of an analyzer 10 attached to the second substrate 5 is perpendicular to the alignment direction of the liquid crystal layer 12. A pair of electrodes 2,3 is formed on the first substrate 1.
In FIG. 1b and FIG. 1d, when the voltage is applied between two electrodes, a horizontal electric field is created. Therefore, the transmittance is controlled by causing the liquid crystal molecules to be rotated to be parallel with the electric field. When the rotation angle of the liquid crystal molecules is 45° in the normally black mode, the retardation value (Δnd) is about λ/2(0.21-0.36 μm) for a maximum transmittance.
In conventional IPS LCDs as described above, the transmittance is controlled by birefringence, and a retardation film is necessary to compensate for the viewing angle which increases the manufacturing cost.
In addition, a viewing angle inverted area appears in the central portion of the outer lines of the display.